linux-kernel - Re: [PATCH v7 11/20] x86/virt/tdx: Add placeholder to construct TDMRs to cover all TDX memory regions

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Date:   Thu, 8 Dec 2022 23:29:37 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "Luck, Tony" <tony.luck@...el.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH v7 11/20] x86/virt/tdx: Add placeholder to construct TDMRs
 to cover all TDX memory regions

On Thu, 2022-12-08 at 06:58 -0800, Dave Hansen wrote:
> On 12/8/22 04:56, Huang, Kai wrote:
> > I haven't looked into the reason yet but I suspect the address isn't aligned (I
> > used __pa() to get the physical address).  I'll take a look and report back.
> > 
> > In the meantime, do you have any comments?  Should I still pursue to keep them
> > as local variable on the stack?
> 
> Yes, you should investigate the reason for the failure and try to
> understand both the success and the failure cases.

Hi Dave,

Learned something new from Kirill today.

The reason is not the alignment, but it's wrong to use __pa() to get the
physical address of function local variable on the stack.  It is because Kirill
told me kernel stack can now be allocated via vmalloc(), so use __pa() won't
work.

I changed to use slow_virt_to_phys() and tried in my testing and it now works.

So I'll change to use slow_virt_to_phys() for the next version.  We can take a
look at the new version to see if that is what you wanted.

Thanks for your time.